The present invention generally relates to compositions produced from solvent exchange processes. In general, the processes replace water in a thiophene mixture with at least one other solvent. A preferred thiophene mixture is a water saturated Baytron(trademark) formulation. Also provided are useful articles including organic solvent based polymeric coatings as well as methods for making and using same.
There is increasing recognition that performance of a wide spectrum of electronic and optical articles can be enhanced by including a conductive molecule. Examples of such articles include anti-static coatings, films, as well as a variety of electronic implementations. See generally Handbook on Conducting Polymers (Skotheim, T. J. ed.) (Dekker, New York, 1986).
Many types of conductive organic molecules have been reported. For example, U.S. Pat. Nos. 6,172,591; 4,237,441; and 5,378,407 disclose organic polymers with a carbon black or metallic conductive filler.
Organic polymers that are intrinsically conductive have attracted substantial interest. Generally, such polymers include sp2 hybridized carbon atoms that have (or can be adapted to have) delocalized electrons for storing and communicating electronic charge. Some polymers are thought to have conductivities neighboring those traditional silicon-based and metallic conductors. These and other performance characteristics make such conductive polymers desirable for a wide range of applications. See Burroughes, J. H. et al. (1986) Nature 335:137; Sirringhaus, H. et al. (2000) Science, 290, 2123; Sirringhaus, H. et al. (1999) Nature 401:2; and references cited therein, for example.
Other conductive polymers have been reported. These polymers include a many optionally substituted polypyrrole, polyaniline, polyacetylene, and polythiophene compounds. See EP-A 302 304; EP-A 440 957; DE OS 4 211 459; U.S. Pat. Nos. 6,083,635 and 6,084,040; and Burroughes, J. H., supra.
There is recognition that many conductive polymers can be used to coat a wide range of synthetic or natural articles such as those made from glass, plastic, wood and fibers to provide an electrostatic or anti-static coating. Typical coatings can be applied as sprays, powders and the like using recognized coating or printing processes.
However there is increasing understanding that many prior conductive polymers are not useful for all intended applications.
For example, many of such polymers are not sufficiently conductive or transparent for many applications. In particular, many suffer from unacceptable conductivity, poor stability, and difficult processing requirements. Other shortcomings have been reported. See e.g, the U.S. Pat. Nos. 6,084,040 and 6,083,635.
There have been attempts to improve some of the prior conductive polymers.
For example, a particular 3,4-polyethylene dioxythiophene (commercially available as Baytron(trademark) P) has been reported to offer good conductivity, transparency, stability, hydrolysis resistance and processing characteristics. See Bayer AG product literature (Edition 10/97; Order No. A1 5593) Inorganics Business Group D-51368, Leverkusen, Germany.
More specific Baytron(trademark) formulations have been reported for use in specific applications.
Illustrative formulations (P type) include CPUD2, CPP103T, CPP105T, CPP116.6, CPP134.18, CP135, CPP 4531I, CPP 4531 E3 and CPG 130.6. Baytron(trademark) M is reported to be a monomer of poly(3,4-ethylenedioxythiophene) and it has been reported to be useful in the manufacture of organic conductive polymers. Further information relating to using Baytron(trademark) formulations can be obtained from the Bayer Corporation, 100 Bayer Rd. Pittsburgh, Pa. 15205-9741. See also the Bayer Corporation website at bayerus.com the disclosure of which is incorporated by reference.
Unfortunately, use of many prior mono- and polythiophene formulations has been problematic.
For example, many important Baytron(trademark) formulations are provided with significant amounts of water solvent. In particular, many Baytron(trademark) P formulations are available as water-saturated colloidal dispersions of the conductive polymer. Typically, a suitable counter ion such as polystyrene sulfonic acid (PSS) is added to the dispersion. There is increasing recognition that many, if not all, Baytron(trademark) formulations would be more useful if means existed for exchanging the water solvent with one or more other solvents of choice.
There have been limited attempts to develop such solvent exchange methods. Nearly all of the attempts have relied on traditional liquid fractionation and distillation schemes. Such approaches have not been able to exchange the solvent for the water in a way that is effective and reproducible.
Flexible electronic device xe2x80x9cwritingxe2x80x9d or xe2x80x9cprintingxe2x80x9d has attracted much recent attention. An example of such a technique involves dispersing an aqueous and conductive thiophene preparation with an ink-jet printer. Typically, poly(3,4-ethylenedioxythiophene) doped with polystyrene sulfonic acid (PEDOT/PSS) is employed. See generally Dagni, R. in Chemistry and Engineering, Jan. 1, 2001, pp. 26-27 as well as references cited therein.
However, these writing or printing procedures have suffered for want of an effective and reproducible means of replacing the water with more useful exchange solvents.
There is recognition that many electro-optic devices, such as light emitting diodes (LED""s) and photovoltaic cells, require electrically conductive and optically transparent films/coatings as electrode materials. Presently, transparent electrodes in electro-optic devices are made of indium doped tin oxide (ITO) coated glass substrates.
However, most prior ITO layers have suffered from shortcomings.
For example, most prior manufacturing processes involving ITO are cumbersome and costly to perform. An illustration is the need to conduct vacuum deposition in a controlled gas atmosphere. Furthermore, most prior ITO films are brittle, difficult to prepare and manipulate, particularly when used in film formats on large area substrates or flexible substrates. See generally Y. Cao, et al. in Conjugated Polymeric Materials: Opportunities in Electronics, Optoelectronics and Molecular Electronics, NATO Advanced Study Institute, Series E: Applied Sciences, J. L. Bredas and R. R. Chance, Eds., Vol. 82, Kluwer Academic, Holland (1990). See also U.S. Pat. No. 5,618,469 and EPO Patent 686,662.
There is belief that certain conducting polymers and coatings may be qualified for some organic light emitting diode (OLED) applications. Briefly, OLEDs are display compositions based on sandwiching deposited organic molecules or polymers between two electrodes. Light emission or luminescence occurs when charged carriers associate with the electrodes recombine and emit light. See U.S. Pat. No. 5,904,961, for instance.
More specifically, a typical OLED includes a metal cathode, electrode transport layer (ETL), organic emitters, the HIL, an ITO anode and glass substrate. Light output passes through the glass substrate.
Electrically conductive and optically transparent coatings have been made with polyaniline (PANI) (U.S. Pat. No. 5,618,469) and PEDOT/PSS polymer dispersion (Eur Patent 686662).
However, many of the prior coatings have recognized drawbacks particularly in relation to OLED applications.
As an example, many have limitations in manufacturing practical electro-optic devices. In particular, it is well known that many PANI systems are not stable. Performance degrades over time. Although there is some understanding that performance of PEDET:PSS-based devices are stable, many prior PEDET/PSS polymers are aqueous based. Fabricating PEDET:PSS coatings onto ITO coated substrates requires cumbersome manufacturing processes. Further, the hydrophilic nature of the PEDOT:PSS system attracts moisture, even through the protective moisture barrier. This characteristic has several disadvantages including premature failure during use.
It would be desirable to have coating and related compositions that are easy to make and use. It would be especially desirable to have solvent-exchanged PEDOT:PSS compositions as well as methods for making and using same that exhibit low resistivity and are suitable for OLED use.
The present invention relates to solvent exchange methods for replacing water in a thiophene mixture. Preferred methods of the invention replace some or all of the water with at least one other solvent. Preferably, the thiophene mixture is a Baytron(trademark) formulation. Also provided are compositions produced by the methods as well as useful articles that include or consist of such compositions. The invention has a wide spectrum of important applications including providing converted (solvent exchanged) Baytron(trademark) formulations for use in consumer goods and electronic writing techniques.
As discussed, it has been difficult to replace the water associated with many thiophene mixtures, particularly but not exclusively, mono- and polythiophene mixtures known as Baytron(trademark) formulations. Such formulations are often provided as collodial or water saturated materials. The present invention addresses this need eg., by providing methods for replacing (exchanging) the water with at least one other more desirable solvent. Significantly, the present methods can be controlled by an invention user so that all or part of the water in mixture is exchanged as needed. Also significantly, the invention can be practiced using standard laboratory equipment, thereby making the invention cost effective in most embodiments. Preferred use of the invention expands the usefulness of thiophene mixtures, particularly the Baytron(trademark) formulations, into applications that heretofore have been difficult or impossible to practice.
The present invention also relates to compositions, preferably polymer coatings, that are easy to make and use. Typically, such compositions are relatively stable and involve use of non- or low toxicity solvents. Preferred compositions according to the invention are PEDOT:PSS compositions, more preferably solvent-exchanged PEDOT:PSS coating compositions suitable for use in a range of electro-optical implemenations including OLEDs.
Such compositions provide advantages including good conductivity, high optical tranparency and environmental stability. Significantly, preferred compositions of the invention can be used to replace indium doped tin oxide (ITO) coated glass substrates that are part of many standard OLEDs.
Also encompassed by the invention are methods for making and using the present compositions. In one embodiment, the methods involve subjecting PEDOT:PSS compositions to conditions that decrease resistivity when compared to (control) compositions not receiving such treatment. Preferred conditions generally involve at least one drying treatment. Also disclosed are methods for making such compositions in which at least one of the method steps involves drying treatment. By the phrase xe2x80x9cdrying treatmentxe2x80x9d is meant exposure to at least one condition that causes, either directly or indirectly, loss of solvent from the composition, preferably exchanged solvent.
The drying treatments provided by the invention provide substantial advantages. In particular, practice of such treatment steps in the methods of the invention provide a straightforward and cost effective way of improving composition performance by assisting solvent loss. Preferred practice involves subjecting conductive coatings of the invention to ambient air and/or heat treatment to help remove solvent, and has been discovered, to help improve performance characteristics such as resistivity. Significantly, such drying treatments are compatible with most manufacturing processes and can be scaled-up as needed. More specific information about the drying treatments is provided in the discussion and examples following.
The invention also features electro-optical implementations that include at least one of the compositions disclosed herein including preferred PEDOT:PSS compositions. An illustration of such an implementation is an OLED or related device. Such OLEDs reduce or avoid use of hard-to-manipulate ITO components while providing coatings with improved performance features, especially resistivity. As provided below, it is an object of the invention to replace prior ITO components with at least one of the compositions of this invention provided as an OLED hole injection layer (HIL).
Accordingly, and in one aspect, the invention provides methods for exchanging (in whole or in part) the water present in a thiophene mixture with at least one other solvent. A preferred mixture includes at least one thiophene, preferably an optionally substituted mono- or polythiophene, more preferably a water saturated Baytron(trademark) formulation. In one embodiment, the method includes at least one and preferably all of the following steps:
a) heating at least one solvent in a vessel under conditions suitable for vaporizing water,
b) contacting the heated solvent with the thiophene mixture (comprising the water and at least one optionally substituted mono- or polythiophene), which contact is sufficient to remove at least part of the water from the mixture as vapor; and
c) exchanging the water removed from the mixture with the solvent.
Preferred practice of the invention involves heating the solvent before contact with the thiophene mixture, although in some invention embodiments substantially contemporaneous solvent heating may be desirable. Preferred heating conditions favor production of water vapor from the mixture. Without wishing to be bound to theory, it is believed that heating the solvent before the contact helps to reduce prolonged contact between the thiophene mixture and the exchange solvent. Such limited contact has many benefits including enhancing water loss from the mixture and increasing exchange with the heated solvent. In contrast, prior practice has been limited to more traditional distillation schemes featuring gradual liquid heating and close solution contact. These schemes are not always designed to minimize contact between the exchanging solvent and the thiophene mixture. Such limited contact is also believed to reduce or avoid binding potential (covalent and non-covalent) between the water and exchange solvent. Such binding is believed to have impeded many past attempts to reduce the amount of or eliminate water from some thiophene mixtures. As will become more apparent from the following discussion, these and other features of the invention provide for more efficient solvent exchange than has heretofore been possible, particularly with many Baytron(trademark) formulations.
Additionally preferred practice of the invention involves maximizing the contact area of the heated solvent with respect to the contact area of the thiophene mixture. Without wishing to be bound to any theory, it is believed that by increasing the heated solvent contact area relative to that of the thiophene mixture, it is possible to boost heat transfer from the exchange solvent to the mixture. In this invention example, the relatively large heated solvent contact area helps to transfer heat quickly and efficiently from the exchange solvent to the mixture. This invention feature also helps to achieve an invention objective ie, the reduction or elimination of unwanted binding between the water and exchange solvent.
The invention provides many other important advantages.
For example, in another aspect, the invention provides highly useful compositions that include or consist of at least one of the converted (solvent exchanged) thiophene mixtures. A preferred converted thiophene mixture is derived from an optionally substituted mono- or polythiophene, particularly a Baytron(trademark) formulation in which the water solvent has been totally or partially replaced with at least one other solvent. In this invention embodiment, it has been found that such converted thiophene mixtures feature better electrical conductivity than corresponding unconverted (control) mixtures. Significantly, such better conductivity is achieved with films and coatings having less thickness than conventional films and coatings made from many Baytron(trademark) formulations. Without wishing to be bound to theory, preferred practice of the invention is believed to provide for more conductive polymer chain orientations. This and other features of the invention will help expand the use of the Baytron(trademark) formulations into a variety of applications in which good conductivity and minimal film or coating thickness is desired.
Turning to the invention methods, it will be understood that it is possible to increase the contact area of the heated solvent by one or a combination of strategies.
For example, in one embodiment, the foregoing solvent exchange method further includes adding about 1 unit volume of the thiophene mixture to more than about one unit volume of the heated solvent e.g., at least about 2 unit volumes of the heated solvent per unit volume of the mixture. The larger heated solvent volume provides the relatively large heated solvent contact area to move heat effectively from the exchange solvent to thiophene mixture.
The heated solvent, thiophene mixture (or both), can be provided in forms so that the heated solvent has a relatively large contact area when compared to the mixture. As an example, the contacting step of the methods can be adapted to include adding the thiophene mixture to the vessel as a flow stream, mist, aerosol; or a combination thereof having the larger contact area.
Typically, but not exclusively, the heated exchange solvent is provided as a pool in the vessel which pool has the relatively larger contact area relative to the added mixture. Addition of that mixture to the vessel can be continuous or discontinuous as needed e.g., as a semi-continuous flow stream or as drops of the mixture added to the pool of heated solvent. In another example, the contacting step of the method includes dispersing the mixture along the surface of the heated solvent. Such dispersal can be continuous or semi-continuous to further assist and maximize the contact area of the heated exchange solvent relative to the thiophene mixture. This example of the invention may be especially useful in instances in which the exchange solvent, the mixture (or both) are available in limited quantities. For some applications, it may be desirable to add the mixture below the surface of the heated solvent.
The methods of the invention are generally flexible and can be used to replace all or part of the water in a subject thiophene mixture with at least one other desired solvent. This feature of the invention further enhances the utility of many optionally substituted mono- and polythiophenes and especially many of the Baytron(trademark) formulations. By way of illustration and not limitation, the invention can be used to replace a pre-determined amount of water in a Baytron(trademark) M or P formulation with at least one other solvent including a combination of different solvents. It is thus possible to make many new thiophene mixtures and particularly a wide variety of converted (solvent exchanged) Baytron(trademark) formulations. Such converted formulations having a pre-determined amount of water exchanged for solvent or combination of solvents can be used in a range of new applications.
As will be appreciated, the invention is compatible with a wide spectrum of solvents. Typically, the exchange solvent will include one solvent. However, for some applications it will be useful to employ a combination of solvents as the exchanging medium e.g, two to six solvents, preferably about two solvents. In another embodiment, the invention methods can be adapted so that all or part of the water in a thiophene mixture is exchanged for a first solvent (or solvent combination). If the resulting converted thiophene mixture includes unexchanged water, that water can be further exchanged (fully or partially) with a second solvent (or solvent combination), thereby making a further converted mixture. Further solvent exchange can be performed as needed. Choice of a particular solvent exchange procedure according to the invention will by guided by recognized parameters including the use for which a particular converted thiophene mixture is intended.
More specific solvents of the invention include those that are stable to heat conditions favoring water vaporization. A more preferred solvent or solvent combination for use in the method has a boiling point of at least about 100xc2x0 C. at standard pressure (1 atmosphere (tam)). However in embodiments in which the water solvent can be vaporized below or above 100xc2x0 C. other solvents may be more desirable e.g, those having boiling points below or above 100xc2x0 C. at 1 atm. Exemplary embodiments include practice of the method in which the vessel has an internal pressure less or greater than about 1 atm. More specific exchange solvent examples include polar and non-polar solvents as well as solvents that are miscible or insoluble in water.
As mentioned, the invention provides compositions made entirely or in part with at least one of the converted (solvent exchanged) thiophene mixtures according to the invention. In one embodiment, the composition is an azeotrope. That is, the composition cannot be separated by fractional distillation into two or more pure substances. Such azeotropes include maximum-boiling azeotropes in which the boiling point of the heated solvent is raised by contact with the water solvent. Also included are minimum-boiling azeotropes in which the boiling point of the heated solvent is depressed by contact with the water solvent.
Preferred compositions of the invention feature an electrical conductivity that is at least about an order of magnitude larger than the corresponding unconverted (no solvent exchange) thiophene mixture when measured according to standard procedures. Particular converted polydioxythiophenes of the invention such as TOR-CP exhibit a conductivity increase that is about one to two orders of magnitude greater than Baytron(trademark) P.
In another embodiment, the invention features more particular methods that include forming a composition from the mixture, preferably a coating composition, and subjecting that composition to at least one drying treatment step as defined herein. Preferably, the drying treatment is performed after step c) of the method (ie. solvent exchange step). Such treatment may be performed once or more than once as needed. More preferred drying treatments involve significant exposure to ambient room temperature or higher temperatures sufficient to remove solvent from the composition. In embodiments in which more than one drying treatment is desired eg., two, three or four of such treatments, the drying treatments may be the same or different as needed to achieve a particular result. In such embodiments, the drying treatments can be performed in a tandem or discontinuous format. Generally, but not exclusively, drying treatments of less than about one to two days are suitable for most invention applications. Less than about several hours, preferably less than a few hours will be preferred for most invention applications. Compositions produced by such methods are also featured herein.
In yet another aspect, the invention provides conductive materials, particularly coating materials and films that include or consist of the compositions provided by this invention. Preferred films suitably include at least one polymer, co-polymer or mixture thereof such as those disclosed below Such conductive materials are well-adapted for use in anti-static or electrostatic applications.
Also featured are conductive coatings that include or consist of the compositions provided herein, preferably configured as a layer having at least one of the following performance characteristics: 1) good resistivity; 2) good surface resistance; and 3) good optical transmission. Preferably, such compositions exhibit at least good resistivity. Examples of preferred conductive coatings are provided in the discussion that follows.
Also provided by the invention are articles of manufacture that include or consist of at least one of the compositions and coating materials of this invention.
In one embodiment, the articles are electro-optical implementations and preferably organic light emitting devices (OLED) such as those provided below.
In another aspect, the invention provides useful methods for making an electronic implementation, typically by xe2x80x9cwritingxe2x80x9d or xe2x80x9cprintingxe2x80x9d, which methods include at least one and preferably all of the following steps:
a) contacting at least one of the compositions disclosed herein with a first polymer layer,
b) dissolving at least a portion of the first polymer layer with the composition under conditions forming a hole, typically a via-hole or interconnect, in the first polymer layer; and
c) evaporating the solvent in the composition to make the electronic implementation.
The foregoing method for making the electronic implementation has important advantages including providing better control of solvent surface tension as well as enhanced writing or printing alignment of the hole. Also provided are electronic implementations and manufactured articles produced by the method.